Photographic developers



United States Patent 3,155,508 PHOTOGRAPHIC DEVELOPERS William Walker, 21 Bentinck St., Calcutta, India No Drawing. Filed Nov. 8, 1960, Ser. No. 67,927 4 Claims. (Cl. 9666) This invention relates to photographic developers. The developer formula plays an important part in the production of the visible picture from the latent image formed on the photographic recording medium, and in order to obtain best results, the developer formula has to be chosen with due regard to numerous considerations such as the temperature of the working developer, the period for which the emulsion may remain in the developer without staining or fogging, whether the finished emulsion silver grain size is fine, large, or medium, for upon this the resolving power depends; whether there is reticulation or softening of the gelatine emulsion, whether the contrast or gradation is hard, medium or normal, etc. A large number of developer formulae are known at present each having the special properties peculiar to itself for producing particular eifects during the development of the latent image.

The normal developer formula contains certain constituents which are (a) the developing agent, (b) the alkali, (c) the preservative, and (d) the restrainer, whose pres ence is essential for the proper functioning of the developing solution.

The developing agent has the capacity to reduce or develop the exposed silver bromide, chloride or iodide grains of the emulsion to metallic silver, thus giving opacity to the negative or positive emulsion. Methyl-para-aminophenol-sulfate, hydroquinone, pyrogallic acid, pyrocatechin, chloroquinol are the names of certain well known developing agents.

The alkali is the energiser of the developing formula, which in simple terms, has the capacity to soften the gelatine emulsion so that the solution may penetrate and allow the developing agent to act quickly on the exposed silver. bromide, silver chloride or silver iodide present in the emulsion. Potassium and sodium carbonate, borax and caustic soda are the usual alkalies employed.

The function of the preservative is to protect the reducing agents from oxidation; sodium sulphite and sodium bisulphite are examples of some of the usual preservatives.

The function of the restrainer is to prevent the reducing agent from developing the unexposed silver grain- Sodium bromide and potassium bromide are two of the restrainers commonly used.

Each developer formula is made up of a certain portion of the abovementioned ingredients in their correct proportions, each of the said ingredients possessing its own velocity or rate of development and its own capacity to influence the photo emulsion.

In the case of every developer, its mode of preparation and processing will determine the nature of the results produced from it; and the various characteristics such as grain, development latitude, film speed, developing time, hardness of the emulsion while in the developer, tone, density, gradation or gamma, e.g. for a film to develop to the maximum degree as regards tonal scale and density, may not be constant for any particular type of emulsion even under similar conditions such as of exposure, temperature,

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and agitation, as they would depend also on the mode of preparation and processing of the developer.

The same formula with a variation in proportion and procedure, will result in a new potentiality. It is not the mere chemical constituents of a developer, but the strength and proportion of each constituent, the mode of its preparation and the mode of the procedure of using it, will elfect the results obtained by it.

Notwithstanding the vast progress made in modern times in evolving developer formulae suited to all conceivable conditions under which the latent image has to be developed, the majority of the developer formulae at present in use have numerous drawbacks, such as those mentioned hereinafter:

(l) The majority of known developers require numerous ingredients for enabling them to function properly.

(2) Known developers are destroyed by oxidation of decomposition when their component chemicals are placed together and boiled for some time.

(3) The developers require careful weighing for correctness. Slightly less or more of even a single chemical produces great changes in the final developing results e.g. a few grains of potassium bromide less or more, the addition or reduction of alkali, methyl-para-amino-phenol-sulfate, hydroquinone or pyro or paraphenylenediamine or other developing agents, radically change the characteristics of the developer formula completely.

(4) Each special type of emulsion requires each special type of developer, and in some cases numerous chemicals might be required for the developer suited to certain emul- SlOIlS.

(5) Prolonged development in other known developers destroy the emulsion.

(6) A line grain developer having a fine grain formula to obtain fine grain results requires longer developing time, e.g. 15 minutes to one hour at F.

(7) Temperature of development must be around 65 F. to obtain best results.

It should be observed that there are three temperatures understood and applied to all photo processes, which are (a) Atmospheric temperature upon which depend the natural room temperature and the solutions in it ie, the

water, the developing, the stop, the hardening and the fixing baths;

(b) The dissolving temperature of the solutions during preparation of the developer at which the chemicals may be or are necessary to be dissolved; and

(c) The development temperature of the developer solution in which the photographic film, plate or paper emulsion is developed.

Therefore from the above observations, temperatures with other known developers are bound by the photographic rules of photo-chemical dissolving and rules of development:

(1) The atmospheric or room, or artificial temperature must be about 65 F. to about F., to obtain satisfactory developing results;

(2) The dissolving temperature of the solution must not 3 the gelatine. The melting or reticulation point of gelatine (in which the silver bromide, chloride or iodide are distributed or emulgated in the emulsion) is from about 75 F. to about 104 F.

(9) Old emulsion and even fresh stock cannot stand long in methyl-para-amino-phenol-sulfate hydroquinone (which will hereinafter be briefly represented by the well known initials MQ) or other developer formulae, unless an antifoggant is used in the developer.

(10) On prolonging the development time threshold fog is comparatively high and there is overall fog and the gelatine in the developed photo emulsion is unstable.

(ll) Staining is caused on very long development time, even of fresh emulsion stock.

(12) Due to the composition of the chemicals in the average developer, they permit only a short limit to the developing time, e.g. only a few minutes, during which the film may be in the developer, and which on prolonged development, will spoil, even at lower tropical warm weather temperatures.

(13) Due to the composition of average developer formulae, there is a tendency to fog and reticulation.

(14) Due to the presence of the developing chemicals in the average developer, a high contrast is built up too quickly and the highligts and brighter middle-tones are clogged up and normally print up chalky if the temperature is higher or developing is prolonged beyond normal.

(15) After the developing time has reached finality, further development of the emulsion will cause stains, fogging, softening of emulsion and reticulation and clogging of the highlights and middle-tones, and rendering it thus unprintable. Therefore, there is no further development capacity to gain more contrast and density after a certain time or by using other developers than those used originally.

(16) Fixing time is prolonged due to formation of complicated salts formed in the emulsion from the developer in the fixer.

(l7) Washing time also is prolonged due to the presence of complicated salts formed during the fixing.

(18) Long immersion in the average developer formula causes softening of the gelatine based emulsion and therefore the drying time is also prolonged.

(l9) Rinsing is necessary for removing the alkali from the emulsion so that the fixing bath which is an acid bath, will not be neutralised; this operation naturally takes up time, and requires space for the rinsing tank or dish.

(20) Due to the presence of chemicals in the emulsion after development from the normal developer, there is slight contamination and neutralisation of the fixing bath during the said rinsing.

(21) As a developing temperature from about 85 F. to about 126 F. or above causes reticulation and softening of the gelatine, therefore the processing time must be shortened; the emulsion would otherwise be exposed to the risk of scratches and marks. A wet photographic film at the higher temperatures is susceptible to scratches and other physical damage.

(22) Developers in the tropics require troublesome and expensive water-cooling and/or air-conditioning appliances, or the use of ice, for the developer temperature to be maintained at around 65 F. For film developing above 75 F., as a rule, additional chemicals, such as glucose, sugar and sodium sulphate are added to prevent the swelling of the gelatine. The use of sodium sulphate will necessitate an increase in the time of development by approximately one third. While the sodium sulphate tends to prevent undue swelling, development must be complete within about 4 minutes, as otherwise the emulsion will fog and soften and swell excessively. Fine grain developers may be employed as tropical developers, provided a similar quantity of sodium sulphate or glucose is added, but most of them prove to have many defects.

(23) Development after the normal time or prolonged developing, increases the size of the grains of the emulsion very greatly. The rule is the longer the developing the larger the grains become.

(24) The keeping properties and the useful storage life of developer solutions are comparatively short e.g. the dish life of the average developer runs from 30 minutes to a maximum of 24 hours and the tank life of the average developer runs fronr3 hours to a maximum of one month.

In opaque stoppered bottles, the lift of the average developer runs from 2 weeks to a maximum of six months.

(25) Developing time is not versatile (development latitude) such as when an average fast film is placed in normal developer, if the development is 15 minutes at 65 F., then prolonging the developing time will cause over development and clogging of the highlights and consequent hardening of the contrasts.

(26) Emulsions according to rules regulating all dcvelopcrs, have to be rinsed after development to prevent contamination of the fixing bath and this gives further reason for softening of the gelatins emulsion and delay during drying in tropical processing.

(27) Sodium snlphite and metl1yl-para-amino-phenolsulfate are in a minor proportion in relation to aqua in the average formulae.

(28) Every known developer allows photo emulsions to stay only a short time e.g. a few minutes to about an hour at a low temperature, length of immersion depending on many factors, including type of emulsion, composition of developer etc.

(29) The developers cannot be used generally on most photographic emulsions.

(30) The prolonged development mentioned above spoils the emulsion by blackening the unexposed grains, reticulation, fogging and complete falling off of the gelatine from its base, and neither can fixation take place in the same developer solution and in one single operation.

(31) Not many developer formulae can be used for redevelopment in intensification, reduction, toning, as stains, fog, reticulation etc. are caused.

(32) The developers are not economical. They quickly get exhausted and quickly oxidise and their dish life is comparatively short. Rinsing of the emulsion is necessary, and alkaline contamination and neutralisation of the fixing bath (which always should give an acid reaction), takes place.

(33) They have not the capacity to bear either extreme and or sudden changes of temperature during development. Reticulation quickly takes place in the gelatine emulsion when either the developer is above normal temperature and/or when the developer solution temperature changes from high to lower or low to higher, the maximum temperature variation for most known developers being about 5 F. to about 15 F. to cause reticulation.

This invention has for its main object an improved photographic developer which will be free from these drawbacks and which will have the following characteristics:

(a) It is made up of ingredients that are easily available.

(b) It can be prepared by a simple process as a single powder by mixing the chemicals in water at short notice by boiling for a short time.

(c) It will not permit harmful oxidation and/or decomposition to take place on boiling.

(d) It is quick working.

(2) It has a long storage life.

(f) It is an ideal tank developer, in addition to possessing excellent qualities for dish developing.

(g) It is non-staining in comparison, on prolonged development, and fog-free.

(h) It prevents the softening of the emulsion even on prolonged development.

(i) The fine grain and the contrast of the visible image can be controlled through short or very prolonged development and agitation, according to type of photo emulsion and contrast required.

(j) It is made up of only two ingredients and may be ready for packing and for use when mixed as a single powder. 4

(k) It is useful and applicable to all types of photographic emulsions tested so far, showing greater advantage in some and lesser in others.

(I) For plates and films, it does not require rinsing between developing hardening and fixing.

(m) It can be used for developing at the tropical and sub-tropical temperature ranging from less than 70 F. to over 126 F. The picture image and contrasts remain soft, the grain fine, the emulsion hard.

(n) Development can go to extreme times and high temperatures, and development forced without similar emulsion fog or reticulation as in other known developers, and can stand sudden and extreme changes of temperature in the developer, without reticulation.

(0) Exposed emulsions may be developed or/ and fixed in the same developing bath in one operation, fixation taking place on prolonged development. This long immersion in the instant tropical thermal developer which completes development and fixation in one operation would prove useful for busy people who cannot afford to spare the time to wait for development of the emulsion to be completed and who do not have the spare time to be present for the full period and at the end of development so that after development has been completed, the emulsion has to be placed into the fixing bath. The busy person may remove his simultaneously developed and fixed emulsion, hours or days after he had placed it in the developing tank, with preliminary agitation.

(p) It is a versatile developer formula where most types of photo emulsions may be developed, and which can be conveniently carried and used by scientists, doctors, travellers, studios, research and other expeditions, X-ray departments, and other laboratories.

With this and other objects in View, this invention consists of a photographic developer comprising a mixture of sodium sulphite, methyl-para-amino-phenol-sulfate and pure water, characterised in that (a) the said three ingredients are present therein the ratio of about 140 to 160 grams of sodium sulphite, 20 to 2% grams of methylpara-amino-phenol-sulfate and 1000 cc. of water, and (b) that the mixture of the said three ingredients is heated from about 210 F. to about 218 F. i.e. from below to above the boiling point for preparing the said developer.

In an improved developer according to this invention, the proportions of sodium sulphite, methyl-para-aminophenol-sulfate and water may range from 14:2:100 re spectively to 1:%:100.

The improved developer may be prepared in pure water, by mixing sodium sulphite then methyl-para-aminophenol-sulfate in order, or by mixing together as one powder sodium sulphite and methyl-para-amino-phenolsulfate, or prepared in the normal way by mixing methylpara-amino-phenyl-sulfate then sodium sulphite, each of the combined mixtures being boiled for about 1 minute to about 30 minutes.

With a developer as described above, the proceeding of emulsions may be done at temperatures from normal summer tropical developing temperatures of about 85 F. to extreme temperatures over 126 F.

A developer according to this invention may be used either by itself or in combination with other well known developers at present in use.

The emulsions developed in this developer according to this invention, are automatically fixed in the developing bath itself, after the normal time of development is completed. Exposures suitable for such comparatively long development technique should be slightly less than normal so that the slower and prolonged development 6 will fix the image, due to slow fixing qualities of tropical thermal developers.

Conditioned tropical thermal developer for fixation of exposed emulsions may be used successfully at the lower temperatures of about 65 F. to about F., combining development cum fixation in the same solution in one operation, and for freshly matured thermal developer, the temperature may be from 85 F. to about F. Combining development cum fixation in the same solution successfully in one operation at the lower warm weather temperatures.

Example 1 A film pack was developed in the tropical thermal developer of the present invention to note reticulation, and capacity to bear great and sudden changes of temperatures while in the tropical thermal developer without reticulating. Thus, the temperature of the developer was at a normal warm Weather tropical shade temperature of 88 F., raised to 100 F. and developed at this temperature for 2 minutes; raised to F. and developed 2 minutes; raised to F. and developed for 3 minutes and 10 seconds and again placed in tropical thermal developer solution which was at 88 F. The solution was then heated and raised to F. and developed for 4 minutes, raised to F. and developed for 4 minutes 20 seconds, and thereafter brought down to 110 F. and developed for 14 minutes. The solution was heated to F. and then raised to 202 F. The emulsion was yet hard at this point of the test. The inherent tropical developing qualities can be appreciated from the labora tory test to determine the melting-point of gelatine. The gelatine is placed in a solution and the solution is heated so that the temperature rises slowly 10 F., each minute. The film is agitated gently at intervals by lifting it out and re-immersing in the solution and the temperature is noted at which the gelatine begins to melt or How away from the film-base. This melting point is a measure of the degree of hardening for standard processing technique. During the latter melting-point test in the present experiment, the emulsion does not get softer, but the reverse result takes place with the emulsion remaining stable and hard, and the melting-point of the gelatine emulsion being raised and strengthened while in the tropical thermal developer.

Example 2 A fast panchromatic film was developed in tropical thermal developer containing 15 parts sodium sulphite, 0.25 part methyl-para-amino-phenyl-sulfate and 100 parts water. The film was developed and fixed within 10 hours, a comparative lowered emulsion sensitivity and a thinner negative resulting.

Example 3 A tropical thermal developer was prepared by admixing 16 parts sodium sulphite, 0.25 part methyl-paraamino-phenol-sulfate and 100 parts water. A panchro matic film was placed in the developer at 100 F. After immersion, the developer was agitated approximately every 2 minutes. In 10 minutes, the negative was developed. The film was kept immersed in the developer and the developer agitated for 2 minutes at 1 hour intervals. The negative was fixed after 4 hours.

From the foregoing examples, it is apparent that the instant developer is extremely versatile and has many unique properties. The present developer can be used in conjunction with presently known developers, as well as alone. As compared with known developers, the novel developers according to the instant invention have ad vantages such as (1) simplicity of formulation, (2) stability to de-composition and oxidation when boiled, (3) permits variation in the formulation, and (4) very short fixing time.

7 8 What I claim is: References Cited in the file of this patent 1. The method of preparing a photographic developer UNITED STATES PATENTS comprising boiling an admixture of from (a) 140-160 parts sodium sulfite, (b) 2.5-20 parts meth'yl-para-amino- 1,933,789 crabtree et a1 7, 1933 phenol-sulfate, and (c) sufiicient water to bring the ad- 5 mixture to 1000 parts. FOREIGN PATENTS 2. The method of preparing a photographic developer ,7 r at Britain Sept. 93 comprising (1) forming a solution of from 140-160 parts 9 ,7 3 rmany J1me 95 sodium sulfite in water, (2) adding from 2.5-20 parts methyl-para-amino-phenol-sulfate to 1) above, (3) ad- 10 OTHER REFERENCES justing the water to obtain a total of 1000 parts solution, Ph t .L b-I d ol 1, Quarterly Supplement N and (4) heating the admixture of 1 and 2 to its boiling 51, page 2 14 (1952), and Quarterly Supplement No. 82, point page 1-07 (1959 The method of Claim 1 wherein the ratio of Wall et a1.: Photographic Facts and Formulas, Amerilmd C is approximately 15111100- 15 can Photographic Publishing Co., Boston, 1947, pages 4. The method of claim 1 wherein the admixture is 54-102, boiled from about one minute to about 30 minutes. 

1. THE METHOD OF PREPAING A PHOTOGRAPHIC DEVELOPER COMPRISING BOILING AN ADMIXTURE OF FROM (A) 140-160 PARTS SODIUM SULFITE, (B) 2.5-20 PARTS METHYL-PARA-AMINOPHENOL-SULFATE, AND (C) SUFFICIENT WATER TO BRING THE ADMIXTURE TO 1000 PARTS. 